Restore type attributes and remove extraneous nullability annotations for Objective-C Mac build

BUG=webrtc:5592
R=tkchin@webrtc.org

Review URL: https://codereview.webrtc.org/1773743002 .

Patch from Jon Hjelle <hjon@andyet.net>.

Cr-Commit-Position: refs/heads/master@{#11922}
diff --git a/webrtc/api/objc/RTCVideoFrame.h b/webrtc/api/objc/RTCVideoFrame.h
index c710290..8ed23ba 100644
--- a/webrtc/api/objc/RTCVideoFrame.h
+++ b/webrtc/api/objc/RTCVideoFrame.h
@@ -11,7 +11,6 @@
 #import <Foundation/Foundation.h>
 
 NS_ASSUME_NONNULL_BEGIN
-// TODO(hjon): Update nullability types. See http://crbug/webrtc/5592
 
 @interface RTCVideoFrame : NSObject
 
@@ -31,7 +30,7 @@
 @property(nonatomic, readonly) int32_t uPitch;
 @property(nonatomic, readonly) int32_t vPitch;
 
-- (nonnull instancetype)init NS_UNAVAILABLE;
+- (instancetype)init NS_UNAVAILABLE;
 
 @end